I have either kept the red booK or Elanco book for as long as i can remember. All calving records and date are put in . When the bulls go in to work and when they come out. Also any appointment i need to keep. When to order feed. and when to order fuel. Even the CPA wants them when we go to tax time. I would be lost without mine. When i am selling bulls or hiefers i have their weights and dates of birth.